Embryonic antigens (EA) are shared by many species, including mice and humans. Tumors of all metazoans tested carry EA and EA expression seems to be a ubiquitous trait of the transformed cell. EA serves as an auto-antigen in syngeneic animal systems when present on developing embryos or on tumors and these antigens elicit a broad array of autochthonous immunological responses in the host which are poorly understood. The work scope of this continuation proposal describes studies aimed at continuing the isolation, localization and characterization of embryonic antigens in chemically and virally induced tumors of rodents. The SV40 and 3 MCA sarcoma systems are used as the primary models. Fetal antigens have been isolated in soluble form from fetal cells and tumor cells and their immunogenicity correlated with antigen dose, timing, and assay system used to monitor tumor resistance induced by immunization with EA from fetal cells and/or tumor cells. New work proposed will focus on continued purification of these antigens. Studies aimed at distinguishing them from TSTA coded for by SV40 or induced by 3 MCA, and discovering the role of soluble EA in activating suppressor cell functions in potentiating tumor progression and the development of embryos and fetuses in pregnant rodents, are described.